Continuous sulphur drossing apparatus

Abstract

Apparatus for the continuous sulphur drossing of lead to reduce its copper content including a plurality of reaction vessels arranged in series, each reaction vessel having a curved bottom and a stirrer for creating a vortex of the contents. Bullion and sulphur are fed into the series through a vortex at controlled rates and through the series at controlled temperatures and a controlled total reaction time, optimally between 8 and 15 minutes. The bullion, dross and unreacted sulphur, if any, are overflowed from vessel to vessel and into an unagitated vessel for separation of the dross and bullion. The bullion feed device splits the undrossed bullion into a metered stream and an unmetered stream, the unmetered stream being utilized to carry away the separated dross for further processing.

We claim: 
     
       1. Apparatus for the continuous sulphur drossing of lead to reduce the copper content thereof which comprises a plurality of reaction vessels arranged in series, a stirring device in each reaction vessel for vigorously agitating the material therein, means for continuously feeding bullion to the first reaction vessel, means for continuously feeding sulphur to the first reaction vessel, a bullion feed rate controlling device for controlling the feed rate of the bullion, a sulphur feed rate controlling device for controlling the feed rate of the sulphur, means for heating the bullion in each reaction vessel, means for controlling the temperature of the bullion in each reaction vessel, means for continuously and concurrently flowing bullion, dross and any unreacted sulphur from each reaction vessel to the next in sequence, without back-mixing, an unagitated separation vessel, means for continuously and concurrently flowing decoppered bullion and dross from the final reaction vessel to the separation vessel, means for scraping the dross from the surface of the decoppered bullion in the separation vessel, and means for continuously withdrawing decoppered bullion from the separation vessel, wherein the bullion feed rate controlling device splits the feed bullion stream into a controlled bullion stream and a variable excess bullion stream, the controlled bullion stream being fed to the series of reaction vessels. 
     
     
       2. Apparatus according to claim 1 and having at least four reaction vessels in series. 
     
     
       3. Apparatus according to claim 1 wherein the means for agitating includes stirring means for forming a pronounced vortex in the bullion in said vessel, and the sulphur being fed to such vessel is introduced into the said vortex. 
     
     
       4. Apparatus according to claim 1 wherein each reaction vessel is provided with a weir over which the materials flow by gravity or pumping to the next vessel in the series. 
     
     
       5. Apparatus according to claim 1 wherein the reaction vessels are zones or compartments in a single unit. 
     
     
       6. Apparatus according to claim 1 wherein each reaction vessel in a separate unit. 
     
     
       7. Apparatus according to claim 1 wherein the dross separation vessel is provided with a mechanical scraper for removing the dross from the surface of the decoppered bullion in said vessel. 
     
     
       8. Apparatus according to claim 7 and having an external launder adjacent to the separation vessel, and a stream of molten bullion flowing in the launder, the dross being caused by the scraper to overflow into the launder where it is collected by the bullion stream therein and removed. 
     
     
       9. Apparatus according to claim 1 and having an external launder adjacent to the separation vessel, and a stream of molten bullion flowing in the launder, the dross being caused by the scraping means to overflow into the launder where it is collected by the bullion stream therein and removed, and wherein the bullion flowing in the launder is the variable excess bullion stream from a bullion feed rate controlling device which splits the feed bullion stream into a controlled bullion stream and a variable excess bullion stream. 
     
     
       10. Apparatus for the continuous sulphur drossing of lead to reduce the copper content thereof comprising: a plurality of reaction vessels arranged in series;   means in each reaction vessel for creating a vortex of the contents of the vessel;   means for continuously metering bullion into the first of the plurality of the reaction vessels at a fixed rate;   means for selectably and continuously feeding sulphur at a controlled rate into the vortex of the first reaction vessel;   the rate of feed of the bullion and the sulphur being set for a total residence time of lead in said reaction vessels of not more than 25 minutes;   means for maintaining and controlling the temperature of each reaction vessel;   means for continuously and concurrently overflowing bullion, dross and any unreacted sulphur from each reaction vessel to the next in sequence without back-mixing;   an unagitated separation vessel;   means for continuously and concurrently overflowing decoppered bullion and dross from the final reaction vessel to the separation vessel; and   means operatively connected with the separation vessel for separating the dross from the decoppered bullion,   wherein the means for continuously metering bullion creates an excess of bullion and wherein said apparatus also includes means for channeling the excess adjacent the separation vessel, and means for combining the separated dross with the excess bullion for carrying away the dross for further processing.   
     
     
       11. The apparatus of claim 10 wherein said total residence time is approximately 8 to 15 minutes. 
     
     
       12. The apparatus of claim 10 wherein the means for creating a vortex includes a downwardly curving lower end of each vessel forming a symmetrically concave portion, and a stirrer having a drive shaft coaxial with the concave portion.